Fluorine molecular laser devices are conventionally known, and, for example, Japanese Patent Laid-open No. 2000-216471 discloses one. FIG. 12 shows a fluorine molecular laser device 101 disclosed in the same Laid-opened Patent, and FIG. 13 shows a constitution of the fluorine molecular laser device 101 seen from a side, which is not disclosed in the same Laid-opened Patent. In FIG. 12 and FIG. 13, the fluorine molecular laser device 101 includes a laser chamber 102 in which a laser gas containing fluorine is sealed, and a pair of main electrodes 104 and 105 for exciting the laser gas by main discharge 150. A one-through fan 114 for leading a flow of the laser gas shown by the arrow 157 to an area between the main electrodes 104 and 105 and a heat exchanger 103 for cooling the laser gas are placed at predetermined positions in the laser chamber 102.
The main electrodes 104 and 105 are placed to oppose each other with the laser gas between them, and cause the main discharge 150 to a discharge space 151 by applying a high-voltage current from a high-voltage power supply 113 to excite the laser gas. A front mirror 106 and a rear mirror 108 are respectively placed in front of and at the rear of the laser chamber 102, and laser light 111 is oscillated in a rightward direction in FIG. 12, which is perpendicular to the main discharge 150. The method for causing the main discharge 150 perpendicularly to an optical axis of the laser light 111 with the main electrodes 104 and 105 being opposed to each other with the laser gas between them as described above is called a lateral excitation type.
As shown in FIG. 13, in the fluorine molecular laser device 101, preionization discharge is performed by preionization electrodes 110 as in an excimer laser device, whereby ultraviolet rays 100 are caused to perform preionization for the discharge space 151. As a result, the laser gas is ionized before the main discharge 150 occurs, and thereby the main discharge 150 is favorably performed. As a result, the laser light 111 with a wavelength of about 157 nm is emitted from the fluorine molecular laser device 101, and is used as a light source for an aligner for lithography, for example, or the like.
However, the prior art disclosed in the aforementioned Japanese Patent Laid-open No. 2000-216471 has the problem described below.
Namely, when the fluorine molecular laser device 101 is used as the light source of an aligner, it is necessary to narrow a spectral line width of the wavelength of the laser light 111 (this is called band-narrowing), and decrease chromatic aberration caused by an optical system of the aligner to improve resolution of exposure. In the conventional fluorine molecular laser device 101, the pressure of the laser gas is about 0.3 MPa to 0.4 MPa (about 3 atmospheres to 4 atmospheres). At such high pressure, pressure broadening in the spectral line width is increased, and the spectral line width of the laser light 111 in a state in which band-narrowing is not performed becomes as wide as about 1 pm. As a result, there arises the problem of reducing resolution of exposure.